A method for the production of 117mSn is irradiation of enriched 116Sn by thermal neutrons in a nuclear reaction 116Sn (n, γ) 117mSn (Mausner et al., Improved Specific Activity of Reactor Produced 117mSn with the Szilard-Chalmers Process, J. Appl. Radiat. Isot., 43, 1117-1122 (1992)). The highest specific activity of 117mSn (ratio of activity to total mass of all Sn isotopes) achieved by this method (neutron flux 2.5·1015 n/(cm2s)) did not exceed 2 Ci/g. This was because of the low cross section in the nuclear reaction 116Sn (n, γ) 117mSn.
Another method is based on the inelastic neutron scattering reaction using enriched 117Sn as a target (nuclear reaction 117Sn (n, n′, γ) 117mSn) (Toporov et al., High Specific Activity Tin-117m Reactor Production at RIAR, Abstracts of the 9th International Symposium on the Synthesis and Applications of Isotopes and Isotopically Labelled Compounds, July 2006, Edinburgh, UK). It requires neutrons with energy higher than 0.1 MeV. Following dissolution of the tin-117 irradiated with a flux 2·1015 n/(cm2s), and chemical purification, 117mSn of specific activity up to 20 Ci/g can be achieved.
These methods result in low specific activity of 117mSn inadequate to scale up to therapeutic doses and too low for radioimmunotherapy (RIT). No carrier added (NCA) isotope is required for these applications. One method that provides 117mSn in NCA form (Mausner et al., Nuclear data for production of 117mSn for biomedical application, J. Radiation Effects, 94, 59-63 (1986)) is irradiation of natural or enriched antimony (Sb) with accelerated protons, dissolution of the irradiated target, and recovery of NCA radioactive tin (radiotin) from the solution. However, the proton current in this method did not exceed 0.15 μA and thus did not result in 117mSn with high specific activity.
In one report cited above (Yu. G. Toporov et al., High Specific Activity Tin-117m Reactor Production at RIAR, Abstracts of the 9th International Symposium on the Synthesis and Applications of Isotopes and Isotopically Labelled Compounds, July 2006, Edinburgh, UK, p. 64), a target prepared of stable enriched metallic 117Sn enclosed in a quartz capsule inside an aluminum container was used to produce radiotin. However, this target when neutron irradiated did not result in specific activity of 117mSn higher than 20 Ci/g.
In another report (Mausner et al., J. Radiation Effects, 94, 59 (1986) cited above), a target made of thin films of antimony (thickness 1-3 μg/cm2), prepared by evaporating antimony onto a copper backing, was used to produce radiotin. The beam current used with this target did not exceed 0.15 μA, and did not result in 117mSn with high specific activity.
In another report (Kurina et al., Device for Producing Radionuclides, Russian Patent No. 2122251 (published Nov. 20, 1998)), a target of irradiated material was inserted into a hermetic shell. However, Sb-target material in this report was not mentioned or considered for use.
Additional methods are thus desirable.